Sarah Nurse, right, of Canada, is congratulated by teammate Laura Stacey after scoring a goal against the United States during the second period of a preliminary round during a women's hockey game at the 2018 Winter Olympics in Gangneung, South Korea, Thursday, Feb. 15, 2018. Canada won 2-1. (AP Photo/Julio Cortez)

GANGNEUNG, South Korea (AP) Meghan Agosta and Sara Nurse each scored in the second period and defending Olympic champion Canada clinched the top spot in pool play by edging the United States 2-1 on Thursday in an early showdown between the dominant powers in women’s hockey.

Genevieve Lacasse made 44 saves, including stopping Hilary Knight at the post inside the final 90 seconds. Brianne Decker hit two posts, the second time coming in the final seconds, before the two rivals ended up in a scrum. Officials reviewed the final play and ruled no goal. The Canadians also had two goals disallowed.

Kendall Coyne scored the lone goal for the Americans.

Canada and the United States are the only countries to ever win gold at the Olympics. The Americans won gold in 1998 when women’s hockey joined the Olympics, while Canada is here looking for a fifth straight gold medal for the country that created the sport.

They played eight times last fall through a pre-Olympic exhibition tour and the Four Nations Cup. The United States won two of the first three, but Canada now has won five straight against their biggest – and only – rival in the sport.

The United States certainly had plenty of chances, including Knight being stopped on a breakaway.

After missing on a penalty shot and hitting a post late in the second, the Americans got on the board when Coyne raced through four Canadians and scored 23 seconds into the third period.

Canada thought briefly it had the first goal of the game with 3:15 left in the first period, but Melodie Daoust and captain Marie-Philip Poulin were in the crease with the play blown dead. The official immediately signaled no goal.

Agosta put Canada up 1-0 at 7:18 of the second on the power play. With Megan Keller in the box for interfering with Poulin, Natalie Spooner in her 100th international game spun and hit Agosta in the slot with a backhanded pass. Agosta’s shot went off Rooney’s glove and in for the goal.

Nurse scored at 14:56 with a shot from the left circle that went off Rooney’s elbow. Laura Stacey appeared to be offside as Canada brought the puck into the zone, but the United States did not challenge.

Officials awarded Jocelyne Lamoureux-Davidson a penalty shot at 16:08 of the second after Canadian forward Haley Irwin placed a glove on top of the puck in the crease amid a pile of bodies in the crease. Lamoureux-Davidson, who scored the fastest back-to-back goals in Olympic history in the U.S. win over Russia, went too slow and got the puck caught near her right foot before a backhand Lacasse easily deflected.

U.S. coach Robb Stauber started Maddie Rooney, his youngest goalie with all three of the U.S. wins against Canada.